This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We have made a mutant Brome mosaic virus (BMV) that has an interesting biological property. The mutations increase the positive charges inside the viral particles through the addition of two alpha-helices in the N-terminal arginine-rich arm in the capsid subunit of BMV. The X-ray crystal structure of the protein shell of BMV has been solved, but there is no information on the inner layer of RNA and how the N-terminal arm interacts with the RNA. We propose a collaboration where we can use cryo-EM to image and reconstruct the wild-type and mutant BMV. We will then trace the N-terminal arm of the two particles and identify how it interacts with RNA. The goal of this project is to visualize this N-terminal arm that is critical for interaction with the packaged viral RNAs and the structure of the RNAs inside the virion.